Biology Reference
In-Depth Information
White Rusts
White rusts are all members of a single genus,
Albugo
, in the Oomycetes and are apparently
obligate parasites like the true rusts. They form
a white blister just underneath the epidermis.
Blisters appear on any part of the plant except
root. They vary in size and shape and are often
confluent in extended patches. There seem to be
two types of infection: general or systemic,
resulting in stunting of entire plant and formation
of pustules on all parts; or local, with direct
invasion of single leaves, stems, or flowers.
Upper surface of leaves often has yellow areas
with white pustules on the underside. The latter
are powdery when mature, and the epidermis
is ruptured to free chains of sporangia that are
carried by wind to moist surfaces. They germi-
nate by 6 to 18 zoospores, swarmspores, which
settle down, produce germ tubes, and enter plants
through stomata.
Stems have localized or extended swellings,
sometimes sharp bends, proliferation from lateral
buds giving a bushy growth. Various flower parts
are deformed with pronounced distortion of
flower pedicels. When these thickened parts die,
oospores are formed to survive the winter in
crop refuse. The disease flourishes in cool, wet
weather; the spores germinate better when
slightly chilled.
Control
Remove infected parts of ornamentals
as noticed. Clean up all vegetable refuse at end of
season and all cruciferous weeds nearby.
Spraying is impractical.
Albugo ipomoeae-panduratae
White Rust
,
general on sweet potato, also on morning-glory,
moonflower,
Jacquemontia
and quamoclit. The
disease is usually late on sweet potato, after vines
have made their growth, but it is very conspicuous
with irregular yellow areas on upper surfaces and
Albugo (Cystopus)
Oomycetes, Peronosporales
Sporangia are borne in chains at apex of a short,
clavate, usually unbranched sporangiophore,
forming a limited sorus beneath the host epider-
mis and exposed by its rupture. The mycelium is
intercellular except for small, knoblike haustoria.
The sporangia dry to a white powder and
are disseminated by wind, germinating by
swarmspores. Fertilization of a globose
oogonium and a clavate antheridium produces a
single oospore, also germinating by swarmspores.
Albugo bliti
White Rust
or
White Blister
on
beet, amaranth, globe amaranth, seabeach ama-
ranth, and smooth pigweed. Blisterlike white pus-
tules formed in leaves change to reddish brown
when mature. Flowers and stems are dwarfed,
distorted. The fungus winters in seed coats.
Destroy infected plants and debris at end of
season. Change location of plantings.
Albugo candida
White Rust
of crucifers on
arugula, cabbage, chinese cabbage, radish, horse-
radish, turnip, watercress, garden cress, pepper-
grass, salsify, mustard, arabis, sweet alyssum,
boerhavia, draba, hesperis, candytuft, stock, wall-
flower and western wallflower.
